The present invention relates generally to the detection of refrigerator doors which have been left open and, more particularly, to a refrigerator door status detection system which is operated by magnetic door sealing strip to signal a user of the refrigerator if a refrigerator door has been left open for a defined period of time.
Detection of the opened/closed status of refrigerator doors is required for the proper operation of a refrigerator incorporating the doors. For example, a blower motor for circulating air within the refrigerator should be operated only while the refrigerator doors are closed to maximize refrigerating efficiency. Similarly, lights for illuminating the food storage compartments of a refrigerator should be turned on only when an associated compartment door is open, otherwise the desired refrigeration temperature may be impossible to maintain. A system for performing these functions is disclosed in U.S. Pat. No. 2,957,320 issued to Armentrout and comprises a switch which is controlled by the force of gravity and by a magnetic field produced by a magnetic door sealing gasket or strip.
Detection of the opened/closed status of refrigerator doors is also beneficial to detect when such doors inadvertently have been allowed to remain open after use of the refrigerator. This detection problem has been addressed in the prior art, for example in U.S. Pat. Nos. 4,241,337 issued to Prada, 4,278,968 issued to Arnett et al, and 4,463,348 issued to Sidebottom.
Prada discloses a system wherein refrigerators are protected by a device which comprises a magnetic sensing switch mounted into the edge of one door and a magnet mounted adjacent the magnetic sensing switch in a kick panel or in the edge of a second door of a two door refrigerator. Whenever the door or one of the two doors is opened, a door ajar signal is activated to visually or audibly alert a user of the refrigerator. Arnett et al. discloses a system wherein a housing including a buzzer and a proximity switch is connected to a wall, for example jof a walk-in freezer, and a magnetic element is secured to an associated door opposite to the proximity switch. Whenever the door is opened, a timer is activated to generate a pulse having a duration equal to an allowed door-open period. Upon detecting the end of the pulse together with continued door-open status, the buzzer is activated. Sidebottom discloses a door monitoring system wherein conventional push button, rocker, or reed switches mounted on a refrigerator or the doors of a refrigerator are monitored to generate visual indicia of the degree of door usage.
Ideally, a refrigerator door ajar system would take advantage of magnetic door sealing gaskets or strips which have been in wide spread use for many years as evidenced by the Armentrout patent. Unfortunately, no commercially successful refrigerator door ajar system based on sensing the magnetic fields generated by the sealing strips has been produced to this time. Such failure is potentially due to the complicated and hence expensive switches which have been used, for example as shown in Armentrout. An additional hindrance to the development of a magnetic strip sensing system has been the tolerances which are present in the manufacture of refrigerators and the extended life of current day refrigerators. In particular, the manufacturing tolerances and potential door sag over the life of a refrigerator allow the positioning of refrigerator doors to vary such that the related positioning of the magnetic sealing strips of the doors can vary by as much as 0.5 inch. Such variations may result in unreliable operation of existing detectors, require detectors which are too expensive to be commercially acceptable or require periodic adjustment which may be difficult, unreliable or impossible in itself and, in any event, is unacceptable both to the consumer and to the manufacturer.
Since none of the prior art systems have gained substantial commercial acceptance in spite of the apparently desireable features of eliminating excessive energy usage and protecting stored food from spoiling, it is apparent that there is a need for an improved door status detection system for use in a refrigerator for sensing a door which remains open for a defined period of time. Such a system must be inexpensive, reliable over time and preferably would be operated from the magnetic sealing strip which is provided on substantially all refrigerator doors.